In a general sense, this invention relates to polymer processing. More specifically, it relates to methods and apparatuses for analyzing spectroscopic properties of the polymer during one of the processing steps.
Plastics, i.e., polymeric resins, are clearly one of the more important materials of use today. Methods for making and using plastics have been well-known for decades. In particular, thermoplastic resins are extremely popular because they can be readily molded into a wide variety of high-quality articles of manufacture. Non-limiting examples of thermoplastic polymers include polycarbonates, polyesters, polyphenylene ethers, styrene resins, acrylic resins, acrylonitrile-butadiene-styrene (ABS) resins, polyamides, polyetherimides, polyphenylene sulfide resins, and various combinations (e.g., copolymers) thereof.
The polymer resins are usually compounded and manufactured as pellets or powders that can be easily shipped to a customer, and/or stored for later processing. In a typical process for many thermoplastics, the base polymer (or multiple polymers) is combined with various other additives in a mixer or extruder. The blended material is then extruded into a water bath, and pelletized. The pellets are then dried in one or more drying operations, and sent to bins for storage, or shipment to a custom molder.
During production, polymer materials often have to be analyzed for a variety of specified characteristics. They include: composition, color, thermal properties, tensile and flexural properties; residual monomer levels, molecular weight, and particle size. The composition and color of the polymer are usually determined by spectroscopic means.
Very often, the color of a polymer is critical for aesthetic appeal, or for properly identifying the particular brand of articles made from the polymer. A desired color for the polymer is usually achieved by incorporating selected pigments and/or colorants into the polymer blend. Great care must be taken to make sure the color matches a specified standard. In these instances, procedures for determining the precise color during polymer processing must be in place.
In a conventional processing system for colored polymers, an operator usually must draw a sample of the polymer as it is extruded, and take it to a laboratory. The sample must then be molded into one or more test plaques. Color measurements are then taken on the plaques, using a calorimeter, for example. If the color conforms to the specification, a signal is given to continue production. If the color is out of specification, the blended polymer mixture must be adjusted (e.g., adjustment of the colorant levels). The reformulated polymer product is then tested again for conformance to the color standard, and the process continues.
While the conventional system for the color-sampling of polymers is adequate in many instances, it is accompanied by some drawbacks. For example, critical production time can be wasted while a sample is drawn and tested in a laboratory. (The polymer extrusion line may have to be slowed down or shut-down during this step). Moreover, the conventional system is at times labor-intensive. For example, one or more individuals may be needed to handle the actual sampling and testing, while additional manpower is required to monitor the production line while the sample is being evaluated. For large-scale polymer production lines, a disruption in the continuity of the overall process can be economically undesirable.
With these concerns in mind, new methods and systems for efficiently carrying out the spectroscopic analysis of a polymer sample would be welcome in the art. The methods should be capable of performing the analysis “on-line”, so that very little production time is lost during the procedure. Moreover, the methods should provide a spectroscopic analysis which generally is as accurate as the analysis performed off-line, e.g., on a test plaque in a laboratory. Furthermore, the methods and accompanying apparatus should be compatible with the other production and processing operations, e.g., drying, pelletizing, and storage operations.